Studies indicate that subscribers are dissatisfied with service when their service requests remain in the queue for too long before they are served. One prior art arrangement for alleviating this problem is to limit the number of subscribers waiting by not entering new identities into the queue, when the number of entries in the queue exceeds a predetermined value. This predetermined value is based on the number of operators presently serving requests and an assumed average rate of service per operator. Whenever the assumed average rate of service differs from the actual rate, the above arrangement incorrectly estimates subscriber delay resulting in inappropriate maximum queue lengths. Additionally, some operator service systems service different types of subscribers having different service acceptability times, i.e., different time delays before service is considered unsatisfactory. No provision is made in the above-mentioned prior art arrangement for accurately determining the maximum queue length when different subscriber types having different service acceptability times are allowed to use the system.
It is a feature in the present invention to control the average time delay of subscribers waiting for service based upon a continuously measured indicator of past service acceptability in such a manner that an accurate maximum queue length can be determined when different subscriber types having different service acceptability times utilize the system.